The pathophysiology of irritable bowel syndrome (IBS) is poorly understood. Epidemology [sic] and physiological studies have suggested a possible role for the intestinal microbiota in the pathophysiology of the disorder. In addition, since IBS is a heterogenous [sic] disorder it is possible that there may be different etiological factors for the different subtypes of this condition;diarrhea-predominant IBS (D-IBS), constipation-predominant IBS (C- IBS), mixed bowel habit IBS (M-IBS). To date, the understanding of the contribution of the intestinal microbiota to the altered intestinal physiology and functional symptoms and the data regarding differences in the intestinal microbiota between the different subtypes of IBS and healthy controls are limited. Our hypothesis for this R03 grant is that the gut microbiota of patients with certain subtypes of IBS is distinct from that of healthy controls. The proposed research project will use a novel approach combining three molecular biology techniques including Terminal-Restriction Fragment Length Polymorphism (T-RFLP) fingerprinting, pyro-sequencing and quantitative polymerase chain reaction (qPCR) to compare the fecal microbiota between patients with different subtypes of IBS and healthy controls. We will study 20 patients from each IBS subgroup and 20 controls. The results of this study will be used as preliminary data for future, in depth, investigations regarding the role of the intestinal microbiota in IBS. If our hypotheses are confirmed, it will provide new insight to the understanding of the disorder and may lead to new mechanistic investigations and hypothesis driven treatments for functional GI disorders by targeting the intestinal flora. The protocols and the results from this study will also provide the basis for future (NIH) grant submissions to further investigate the role of intestinal bacteria in these disorders. PUBLIC HEALTH RELEVANCE: Irritable Bowel Syndrome (IBS) is a gastrointestinal disorder of unknown cause and can occur as diarrhea, constipation or mixed bowel habit IBS (D-IBS, C-IBS and M-IBS). Recent studies point to an association of the bacteria in our intestine (the intestinal microbiota) with this disorder. The hypothesis of this study is that the intestinal microbiota of patients experiencing D-IBS, C-IBS or M-IBS is different to the microbiota of healthy people. This study will use advanced molecular techniques to analyze the gut microbiota in patients experiencing different subtypes of IBS and healthy people. This study will investigate the role of the intestinal microbiota in IBS. Additionally, this study will provide insight to the understanding of IBS and my lead to new treatments for functional gastrointestinal disorders.